Implantable cardiac devices provide patients with automatic monitoring of cardiac activity and delivery of programmed therapy upon detection of certain cardiac arrhythmia's. The initial and ongoing clinical care provided to patients with implantable cardiac device systems often includes the use of programmers. Implantable cardiac devices are typically provided with telemetry circuits and programmers are devices that enable a clinician to telemetrically communicate with and control an implantable cardiac device, such as a pacemaker or defibrillator.
Implantable devices often monitor and record a variety of internal physiological parameters of the patient as well as data relating to device operation and status and periodically telemetrically transmit this measured and recorded information outside the patient's body to a programmer. Programmers are generally provided with displays to allow a clinician to review the data via the programmer and make any indicated changes in the patient's therapy.
One common type of internally monitored information telemetrically provided by an implantable device for display on a programmer is provided as waveforms derived from electrical cardiac signals obtained internally, typically via leads directly on or within cardiac tissue, and variously referred to as intracardiac electrograms (IEGM) or electrograms, egrams, or EGMs. The IEGM waveform indicates internally measured propagation of low amplitude electrical signals, commonly referred to as the cardiac impulse, across the myocardium giving information about depolarization and repolarization characteristics of the heart.
The ongoing clinical care provided to patients with implantable cardiac device systems also often includes the use of surface electrocardiograms (ECG). The ECG also provides information regarding propagation of the cardiac impulse, however, as measured on the skin surface of the patient. A surface ECG is a highly useful diagnostic aid for clinicians for the study of heart rate and rhythm and to confirm proper operation of the implantable device's sensing function via comparison with the device generated IEGM signal.
An ECG is typically obtained from signals from a plurality of electrodes (3, 5, and 12 are common numbers) that are placed on the patient's skin surface. The ECG indicates monitored voltage signals appearing between various pairs of the electrodes and reflects a vector analysis of the resultant signal pairs to prepare various two-dimensional voltage-time graphs indicative of internal cardiac activity. Again, surface ECG refers to placement of electrodes on the surface, or skin, of the patient as opposed to directly to cardiac tissue as in an IEGM.
Additional implantable sensors are known and can provide additional information to an implantable cardiac stimulation device relating to metabolic need, patient activity level, patient orientation, etc. to further refine the delivery of appropriate therapy. For example, O2 saturation sensors can provide information relating to metabolic utilization of blood oxygen that can indicate a change in pacing rate. 3-D accelerometers can provide information relating to both patient orientation (supine, standing, etc.) as well as activity level (still, walking, running, etc.) that can also indicate a change in therapy delivery. Sensors are also available that can provide quantitative information on respiration rate and depth also indicative of metabolic need.
Current telemetry typically operates at 8k and can accommodate up to two channels of IEGM data, along with one frame of event markers. Markers are real-time annotations of paced and sensed events and can be graphically displayed concurrent with a surface electrocardiogram (ECG) waveform and/or an IEGM waveform via the display of a programmer. The IEGM data is generally composed of four frames of data. The two channels can be sampled at 256 bytes/second, with each channel using two frames. Alternatively, a single IEGM channel can be sampled at 512 bytes/second using all four frames for the single channel.
It is desirable to be able to provide a clinician with as much and as detailed information as possible, however, it will be understood that bandwidth limitations limit the amount/rate at which data can be transferred. In particular, an 8k telemetry system is typically limited to providing only the IEGM and marker information identified above with data related to device performance/operation. Thus, other sensor data that may be available to the implantable device is typically not available on a real-time basis to the clinician.
Real-time data is preferred as it provides useful detail that can be lost in a derived value, such as a total count or average value. Real-time data also enables a clinician to compare internally monitored data with direct observation of the patient and/or other data such as from surface monitoring. However, in certain applications, it can be desirable to have a quasi-real-time presentation of data to enable processing of raw data so as to obtain, for example, marker data, a rate, or an average value or to present waveforms in frames. With available processing means, this level of processing can generally provide information that on the scale of human perception is indistinguishable from true real-time presentation.
It will be understood that telemetry rate is generally dependent on available power. Implantable devices are typically battery powered and increasing telemetry rate typically increases power drawn from the battery thereby reducing battery life, often to an undesirable degree. Replacement of a depleted battery typically requires an invasive explantation procedure and is thus desirably extended as long as possible. In addition, for many currently used technologies, the battery directly powers the device (typically referred to as an unregulated device). Increasing the power drawn from the device reduces the available battery voltage which can impair device operation.
From the foregoing, it can be understood that there is an ongoing need for an implantable device programmer system that can provide a clinician with additional diagnostic information of multiple internally monitored physiological parameters on a real-time basis.